The Environmental Protection Agency has fined the Ross Valley Sanitary District $16,250 for improperly using crushed concrete coated with paint containing PCBs as backfill at its former wastewater treatment plant in Larkspur.

The PCBs — polychlorinated biphenyls — found at the site at 2000 Larkspur Landing Circle were an additive to the paint that was used on buildings at the district's old treatment plant. The facility was demolished "around 1998 or 1999," according to the EPA.

In a press release, the EPA said, "The site is currently vacant, and preventive measures have been taken to ensure contamination backfill materials will not migrate offsite."

Greg Norby, the district's interim general manager, said the PCBs at the site "are not at all like the liquid PCBs found in old electrical transformers. It is not what they call bioavailable, and it cannot migrate."

The EPA said the district first became aware of the presence of PCBs in its crushed concrete after receiving a cleanup order from the California Department of Toxic Substances Control in 2008.

The district dropped efforts to clean up the site after Campus St. James Larkspur LLC pulled out of an agreement to pay the district $12 million for the rights to develop the property.

Campus sued the district, asserting that it contaminated the land with PCBs while conducting demolition and grading operations, and the district eventually agreed to pay Campus $4.75 million to settle the lawsuit.